As is well known, Fibre Channel (FC) is an American National Standards Institute (ANSI) standard specifying a bidirectional serial data channel, structured for high performance capability. Physically, the Fibre Channel may be viewed as an interconnection of multiple communication points, called N_Ports, interconnected by a link comprising a switching network, called a fabric, or a point-to-point link. Fibre is a general term used to cover all physical media types supported by the Fibre Channel, such as optical fibre, twisted pair, and coaxial cable.
The Fibre Channel provides a general transport vehicle for Upper Level Protocols (ULPs) such as Intelligent Peripheral Interface (IPI) and Small Computer System Interface (SCSI) command sets, High-Performance Parallel Interface (HIPPI) data framing, IP (Internet Protocol), IEEE 802.2, and others. Proprietary and other command sets may also use and share the Fibre Channel, but such use is not defined as part of the Fibre Channel standard.
Fibre Channel is structured as a set of hierarchical functions denoted FC-0, FC-1, FC-2, FC-3 and FC-4.
FC-0 defines the physical portions of the Fibre Channel including the fibre, connectors, and optical and electrical parameters for a variety of data rates and physical media. Coax and twisted pair versions are defined for limited distance applications. FC-0 provides the point-to-point physical portion of the Fibre Channel. A variety of physical media is supported to address variations in cable plants.
FC-1 defines the transmission protocol which includes the serial encoding, decoding, and error control.
FC-2 defines the signaling protocol which includes the frame structure and byte sequences.
FC-3 defines a set of services which are common across multiple ports of a node.
FC-4 is the highest level in the Fibre Channel standard. It defines the mapping, between the lower levels of the Fibre Channel and the IPI and SCSI command sets, the HIPPI data framing, IP, and other ULPs.
Additional details regarding these and other aspects of Fibre Channel can be found in the ANSI Fibre Channel standard documents, including the FC-PH, FC-FS, FC-AL-2, FC-PI, FC-DA, FC-MI and FC-LS documents, all of which are incorporated by reference herein.
In typical conventional practice, Fibre Channel links are designed to operate at data rates of 4.25 Gbps, 2.125 Gbps or 1.0625 Gbps. Although higher data rates are possible, the industry is reluctant to spend money upgrading existing hardware to implement these higher data rates. The problem is that as data rates increase, to the proposed Fibre Channel rates of 8.5 Gbps, 17 Gbps and higher, the existing hardware degrades the electrical signals. As a result, it may be difficult to achieve desired levels of performance without the use of sophisticated transmit and receive equalization techniques.
Fibre Channel currently utilizes a non-return-to-zero (NRZ) signaling format, in which a single bit is transmitted per clock cycle. However, increasing the data rate beyond the 4.25 Gbps supported by the existing standard, while continuing to use NRZ signaling, will require a substantial increase in the size and power consumption of the physical layer (PHY) hardware, and thus may not be cost effective. This is particularly problematic in the case of application specific integrated circuits (ASICs) or other implementations involving large channel counts, for example, channel counts between about eight and 100, where the PHY hardware size and power will typically be dominated by the Serializer/Deserializer or “SerDes.”
Accordingly, improved signal transmission techniques are needed, for use in Fibre Channel or other serial data channels, so as to accommodate higher data rates while avoiding substantial increases in the size and power consumption of the SerDes and other physical layer hardware.